U.S. patent number 4,968,581 [Application Number 07/361,985] was granted by the patent office on 1990-11-06 for high resolution photoresist of imide containing polymers.
This patent grant is currently assigned to Hoechst Celanese Corporation. Invention is credited to Michael J. McFarland, Anne M. Mooring, Christopher E. Osuch, Chengjiu Wu, James T. Yardley.
United States Patent |
4,968,581 |
Wu , et al. |
* November 6, 1990 |
High resolution photoresist of imide containing polymers
Abstract
Photoresist compositions suitable for deep UV and excimer laser
lithography are disclosed that are mixtures of a photoacid and a
polymer having imide residues to which acid labile groups are
attached. These compositions provide high resolution, high contrast
and high sensitivity in the deep UV (wavelength of 250-300 nm),
mid-UV (wavelength of 300-350 nm) or conventional (wavelength of
350-450 nm) exposure bands. The compositions are also suitable for
exposure at wavelengths commonly associated with excimer laser
sources (248, 308 nm) or for exposure by X-radiation. In the
compositions disclosed, the imide group ##STR1## can be blocked
with certain groups, X, to form compounds containing the structure
##STR2## which have solubility properties different from the
unblocked imide. These groups, X, can be cleaved by acid under the
proper conditions to regenerate the unblocked imide. Also, where
the imide group is incorporated in a polymer, the polymer with
blocked imide groups can be made to function as a resist when
compounded with a substance capable of forming an acid upon
exposure to radiation. The exact nature of the imide containing
polymer is not critical, providing that: (1) in the unblocked
state, the polymer is completely soluble in aqueous alkali; (2) in
the blocked state, it is insoluble in the same aqueous solution,
while simultaneously; (3) in the blocked state, it is soluble in a
solvent capable of dissolving a suitable sensitizer; and (4) it is
film forming. Other secondary properties may be selected (to
enhance the characteristics of the resist) by varying the structure
of the imide or a comonomer.
Inventors: |
Wu; Chengjiu (Morristown,
NJ), Mooring; Anne M. (Morristown, NJ), McFarland;
Michael J. (Middlesex, NJ), Osuch; Christopher E. (Mine
Hill, NJ), Yardley; James T. (Morristown, NJ) |
Assignee: |
Hoechst Celanese Corporation
(Somerville, NJ)
|
[*] Notice: |
The portion of the term of this patent
subsequent to June 6, 2006 has been disclaimed. |
Family
ID: |
27001504 |
Appl.
No.: |
07/361,985 |
Filed: |
June 6, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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832116 |
Feb 24, 1986 |
4837124 |
|
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Current U.S.
Class: |
430/192; 430/193;
430/270.1; 430/325; 430/326; 430/330; 52/31; 52/32; 522/152;
522/31; 522/32 |
Current CPC
Class: |
G03F
7/004 (20130101); G03F 7/0233 (20130101); G03F
7/039 (20130101) |
Current International
Class: |
G03F
7/023 (20060101); G03F 7/004 (20060101); G03F
7/039 (20060101); G03C 001/54 (); G03C 001/56 ();
G03C 001/73 (); G03C 005/16 () |
Field of
Search: |
;430/270,193,192,326,325,330 ;522/31,32,152 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
W S. DeForest, Photoresist: Materials and Processes, McGraw-Hill
Book Company, New York, N.Y., 1975, pp. 93-103, 132-147..
|
Primary Examiner: Hamilton; Cynthia
Attorney, Agent or Firm: Roberts; Richard S.
Parent Case Text
This is a divisional of co-pending application Ser. No. 06/832,116
filed on 2/24/86 now U.S. Pat. No. 4,837,124.
Claims
What is claimed is:
1. An article comprising a substrate and a dried photoresist
composition on the substrate, the photoresist composition
comprising a mixture of:
(a) from 1 to 50% by weight of a latent photoacid; and
(b) from 50 to 99% by weight of a film forming imide containing
polymer having a sufficient number of imide N-H groups replaced by
acid labile groups to render the polymer insoluble in aqueous
alkali, the composition comprising a solvent which dissolves both
the latent photoacid and the polymer.
2. A method of producing a positive tone relief image on a
semiconductor substrate comprising forming a photoresist
composition comprising a mixture of:
(a) from 1 to 50% by weight of a latent photoacid; and
(b) from 50% to 99% by weight of a film forming imide containing
polymer having a sufficient number of imide N-H groups replaced by
acid labile groups to render the polymer insoluble in aqueous
alkali; coating the composition on a semiconductor substrate;
drying the composition; imagewise exposing the composition to
imaging radiation; deblocking at least a portion of the imides; and
developing the composition with an aqueous alkaline developer to
thereby produce a positive relief image.
3. A method of producing a negative tone relief image on a
semiconductor substrate, comprising forming a photoresist
composition of comprising a mixture of:
(a) from 1 to 50% by weight of a latent photoacid; and
(b) from 50 to 99% by weight of a film forming imide containing
polymer having a sufficient number of imide N-H groups replaced by
acid labile groups to render the polymer insoluble in aqueous
alkali; coating the composition on a semiconductor substrate;
drying the composition; imagewise exposing the composition to
imaging radiation; deblocking at least a portion of the imides; and
developing the composition with an organic non-polar developer to
thereby produce a negative relief image.
4. An article which comprises a substrate and a dried light
composition on said substrate, which composition comprises
(i) from 1 to 50 by weight percent of a latent photoacid and
(ii) from 50 to 99 by weight percent of a film forming imide
containing polymer having a sufficient number of imide N-H groups
replaced by acid labile groups to render the polymer insoluble in
aqueous alkali.
5. The article of claim 4 wherein the latent photoacid is an
iodonium salt.
6. The article of claim 5 wherein the iodonium salt is selected
from the group consisting of a diphenyl iodonium salt, a
4-methylphenyl iodonium salt, and a 4-methoxyphenyl iodonium
salt.
7. The article of claim 6 wherein the iodonium salt is selected
from the group consisting of diphenyl iodonium triflate;
di-4-methylphenyl iodonium triflate; and (4-methoxyphenyl)phenyl
iodonium triflate.
8. The article of claim 4 wherein the latent photoacid is a
sulfonium salt.
9. The article of claim 8 wherein the sulfonium salt is selected
from the group consisting of a phenyl sulfonium salt; a
methylphenyl sulfonium salt, and a 4-methoxyphenyl sulfonium
salt.
10. The article of claim 9 wherein the sulfonium salt is a
triphenyl sulfonium triflate.
11. The article of claim 4 wherein the latent photoacid is a
diazonaphthoquinone.
12. The article of claim 11 wherein the diazonaphthoquinone is
2,4-bis(1,2-dihydro-1-oxo-2-diazonaphthalene-4-sulfonato)benzophenone.
13. The article of claim 4 wherein the imide containing polymer
contains succinimide or glutarimide residues.
14. The article of claim 13 wherein the imide containing polymer is
poly-co(maleimide styrene) or poly-co(maleimide-4-tertbutyl
styrene).
15. The article of claim 14 wherein 50 to 100% of the imide of N-H
groups are replaced with acid labile groups.
16. The article of claim 13 wherein the acid labile group is an
oxycarbonyl group.
17. The article of claim 16 wherein the oxycarbonyl group is
tert-butoxy carbonyl or benzyloxy carbonyl.
18. The article of claim 4 wherein the imide containing polymer
contains acyclic imide residues.
19. The article of claim 18 wherein in 50 to 100% of the imide N-H
groups are replaced with acid labile groups.
20. The article of claim 19 wherein the acid labile group is an
oxycarbonyl group.
21. The article of claim 4 wherein a sensitizer capable of
transferring energy to the latent photoacid is incorporated in the
composition.
22. A method of producing a positive or negative image which
comprises
(a) forming a composition comprising
(i) from 1 to 50 weight percent of a latent photoacid and
(ii) from 50 to 99 weight percent of a film forming imide
containing polymer having a sufficient number of imide N-H groups
replaced by acid labile groups to render the polymer insoluble in
aqueous alkali, the composition being dissolved in a solvent which
dissolves both the latent photoacid and the polymer; and
(b) coating said composition on a substrate to form a substantially
uniform film of the composition on the substrate; and
(c) heating said composition for a sufficient time and at a
sufficient temperature to substantially dry the composition;
and
(d) imagewise exposing the composition to sufficient imaging energy
to form a latent image; and
(e) developing the composition with an aqueous alkaline solution to
form a positive image or an organic nonpolar solvent developer to
obtain a negative image.
23. The method of claim 22 wherein the latent photoacid is an
iodonium salt.
24. The method of claim 22 wherein the iodonium salt is selected
from the group consisting of a diphenyl iodonium salt, a
4-methylphenyl iodonium salt, and a 4-methoxphenyl iodonium
salt.
25. The method of claim 24 wherein the iodonium salt is selected
from the group consisting of diphenyl iodonium triflate;
di-4-methylphenyl iodonium triflate; and (4-methoxyphenyl)phenyl
iodonium triflate.
26. The method of claim 22 wherein the latent photoacid is a
sulfonium salt.
27. The method of claim 26 wherein the sulfonium salt is selected
from the group consisting of a phenyl sulfonium salt; a
methylphenyl sulfonium salt, and a 4-methoxyphenyl sulfonium
salt.
28. The method of claim 27 wherein the sulfonium salt is a
triphenyl sulfonium triflate.
29. The method of claim 22 wherein the latent photoacid is a
diazonaphthoquinone.
30. The method of claim 29 wherein the diazonaphthoquinone is
2,4-bis(1,2-dihydro-1-oxo-2-diazonaphthalene-4-sulfonato)benzophenone.
31. The method of claim 22 wherein the imide containing polymer
contains succinimide or glutarimide residues.
32. The method of claim 31 wherein the imide containing polymer is
poly-co(maleimide styrene) or poly-co(maleimide-4-tert-butyl
styrene).
33. The method of claim 32 wherein 50 to 100% of the imide N-H
groups are replaced with acid labile groups.
34. The method of claim 31 wherein the acid labile group is an
oxycarbonyl group.
35. The method of claim 34 wherein the oxycarbonyl group is
tert-butoxy carbonyl or benzyloxy carbonyl.
36. The method of claim 22 wherein the imide containing polymer
contains acyclic imide residues.
37. The method of claim 36 wherein 50 to 100% of the imide N-H
groups are replaced with acid labile groups.
38. The method of claim 37 wherein the acid labile group is an
oxycarbonyl group.
39. The method of claim 22 wherein a sensitizer capable of
transferring energy to the latent photoacid is incorporated in the
composition.
Description
The invention relates to photoresist compositions suitable for deep
UV and excimer laser lithography. The photoresist compositions are
mixtures of a photoacid and a polymer having imide residues to
which acid labile groups are attached. These compositions provide
high resolution, high contrast and high sensitivity in the deep UV
(wavelength of 250-300 nm), mid-UV (wavelength of 300-350 nm) or
conventional (wavelength of 350-450 nm) exposure bands and are also
suitable for exposure at wavelengths commonly associated with
excimer laser sources (248, 308 nm) or for exposure by
X-radiation.
BACKGROUND OF THE INVENTION
Presently available resists usually have one or more drawbacks. For
example, most negative acting resists have limited resolution
because they swell upon development or, in the case of positive
acting, novolac resin based resists, are formulated from materials
which are opaque at the shorter wavelengths needed for high
resolution work, or are very insensitive as in the case of positive
acting, polymethyl methacrylate based resists.
Some problems and recent developments associated with high
resolution lithography are described, for example, by M. J. Bowden
(ACS Symposium Series 266, American Chemical Society, Washington,
D.C. 1984, p. 39-117).
Processes have been developed to circumvent these problems
(multi-level resists), but they are complex and require an increase
in the number of steps per device layer. An ideal resist would be a
single layer which could be exposed with deep UV light (250 to 300
nm) (DUV), X-rays, or electron beam radiation.
In addition to high resolution, which is a measure of how small a
structure can be created in the resist, high contrast (defined for
a resist as a measure of the resist's sensitivity to changes in
exposure dose) is a desirable feature for high resolution resists.
This is true because the image formed by the exposure tool is not
perfect but has a contrast (defined for the tool as the sharpness
of its image) limited by the laws of optics and the size of the
structure to be reproduced. The resist must correct the fuzziness
of the projected image to give a structure of proper size with
sharp vertical walls. This is particularly important for structures
having widths less than 11/2.mu. meter, since the resist film is
typically 1 to 11/2.mu. meter thick. If the resist wall is not
vertical, any subsequent process step which erodes a portion of the
resist surface, such as reactive ion etching, will change the width
of the structure which in turn can have a deleterious effect on the
circuit being produced. The higher the contrast of a resist the
more the resist can correct for low contrast in the projected
image, and the smaller will be the features of an image which can
be successfully exposed to give a usable structure.
High sensitivity is also an essential property of a high resolution
resist. The economics of semiconductor device manufacture require
high throughput. This means that the time taken to expose each
wafer must be minimized. As a result, the exposure energy per unit
area of resist is constrained. Furthermore, some exposure tools
have less total energy available in the bands used to achieve high
resolution than they have in their conventional, low resolution
exposure bands. This further reduces the energy available at the
wafer suface.
The use of cationic photoinitiators (such as those disclosed in
U.S. Pat. Nos. 3,981,897; 4,450,360; or 4,374,086) to cleave
polymer pendant groups so as to change the polymer structure to an
extent sufficient to create significantly different solubility
characteristics in the irradiated and unirradiated areas is
disclosed in U.S. Pat. No. 4,491,268. The polymers described as
useful in U.S. Pat. No. 4,491,268 are blocked poly-4-hydroxy
styrenes, a blocked poly 4-vinylbenzoate, blocked
poly-isopropenylphenyloxyacetates or blocked poly-methacrylates.
The blocking groups said to be useful included a wide range of acid
labile groups, such as trityl, benzyl or tert-butoxy. This includes
structures such as ##STR3## where X and Y are acid labile blocking
groups, e.g., ##STR4## Y. The structures of the deblocked polymers
present after irradiation and baking are respectively.
In short, there is a need for new resists having high sensitivity,
high contrast and high resolution. The need arises from the desire
of semiconductor manufacturers to produce structures smaller than
11/4 .mu.m in width.
SUMMARY OF THE INVENTION
The present invention provides for a resist having high contrast,
high sensitivity, and high resolution which may be exposed by
X-radiation, electron beam radiation, and particularly by
ultraviolet light in the wavelength region from 250 nm to 350
nm.
In accordance with the invention, we have found that the imide
group ##STR5## can be blocked with certain groups, X, to form
compounds containing the structure ##STR6## which have solubility
properties different from the unblocked imide. These groups, X, can
be cleaved by acid under the proper conditions to regenerate the
unblocked imide. Where the imide group is incorporated in a
polymer, the polymer with blocked imide groups can be made to
function as a resist when compounded with a substance capable of
forming an acid upon exposure to radiation. The exact nature of the
imide containing polymer is not critical, provided that: (1) in the
unblocked state, it is completely soluble in aqueous alkali; (2) in
the blocked state, it is insoluble in the same aqueous solution
while simultaneously; (3) in the blocked state it is soluble in a
solvent capable of dissolving a suitable sensitizer and finally;
(4) in the blocked state it should be film forming. There are other
secondary properties which may be selected (to enhance the
characteristics of the resist) by varying the structure of the
imide or a comonomer.
DETAILED DESCRIPTION OF THE INVENTION
In the invention, we have discovered that the imide group ##STR7##
can be blocked with certain groups, X, to form compounds containing
the structure ##STR8## which has solubility properties different
from the unblocked imide, and that these groups, X, can be cleaved
by acid under the proper conditions to regenerate the unblocked
imide. Furthermore, if the imide group is incorporated in a
polymer, the polymer with blocked imide groups can be made to
function as a resist when compounded with a substance capable of
forming an acid upon exposure to radiation. We have found that the
exact nature of the imide containing polymer is not critical,
providing that certain properties are observed, i.e.: (1) in the
unblocked state, the polymer should be completely soluble in
aqueous alkali; (2) in the blocked state, the polymer should be
insoluble in the same aqueous solution, while simultaneously; (3)
in the blocked state the polymer should be soluble in a solvent
capable of dissolving a suitable sensitizer, and finally; (4) in
the blocked state, the polymer should be film forming. However,
there are other secondary properties which may be selected (to
enhance the characteristics of the resist) by varying the structure
of the imide or a comonomer.
The imide containing polymer may have the structures ##STR9## where
the imide moiety is contained in the polymer backbone itself. If
this is the case, the blocked imide containing polymers will have
the structures ##STR10## respectively.
Alternatively, the imide moiety may be pendent from the polymer
backbone such as in the structures ##STR11## where the blocked
polymer will have the structures ##STR12## respectively, where R is
an alkyl or aryl group. The imides may have a cyclic structure
which results in a blocked polymer having the structure ##STR13##
in the case of a polymer where the imide is in the backbone or such
as ##STR14## where R is alkyl or aryl or H, in the case of a
pendent imide. In all these cases, n and p are from 0 to 10 and m
varies with the degree of polymerization and may be from 5 to
100.
Ease of preparation will naturally favor certain structures over
other. For example, polymaleimide ##STR15## or a polyglutarimide,
such as that of Gleim, et al. (U.S. Pat. No. 4,524,121) ##STR16##
may be selected as the parent imide to give the blocked polymers
##STR17## where X is the acid labile blocking group. Alternatively,
for a fixed imide structure the kind and amount of non-imide
structure incorporated into the polymer may be varied. For example,
a copolymer of maleimide and a styrene ##STR18## or maleimide and a
vinyl ether ##STR19## can be blocked to give ##STR20##
respectively, where X is an acid labile blocking group and R is an
alkyl or aryl group.
The acid labile group X should be reasonably stable at 100.degree.
C., to permit baking of freshly spun resist films to remove
solvent. Furthermore, it must not react with the developer or
sensitizer in such a way as to render the resist functionally
inoperative. From the known set of acid labile protecting groups
the groups found to be most effective are oxycarbonyl groups,
##STR21## where R is an alkyl, aryl, or substituted alkyl or aryl
group. The preferred acid labile group for this invention is
tert-butoxy carbonyl ##STR22## which has been found to be easily
attached to preformed imide containing polymer and is stable at
temperatures below about 110.degree. C. This group is not readily
attacked by aqueous alkali nor is it reactive in the presence of
unexposed, latent photoacid.
The latent photoacid may be selected from a wide range of
substances known to form acids upon irradiation including
diazoketones, such as diazonaphthoquinones ##STR23## or
5-diazobarbituric acid derivatives, disclosed in the co-pending
U.S. patent application Ser. No. 805,641 filed on Dec. 6, 1985,
such as ##STR24## where R.sub.1 and R.sub.2 are either sulfonyl
moieties ##STR25## or H (but not the same) and R.sub.3, R.sub.4 and
R.sub.5 are alkyl or aryl groups. Additionally, "onium" salts such
as diazonium, iodonium or sulfonium salts may be used as the
photoacids in this invention, e.g.,
R.sub.6 N.sub.2.sup.+ Y.sup.-, (R.sub.6).sub.2 I.sub.2.sup.+,
(R.sub.6).sub.3 S.sup.+ Y.sup.-
where R.sub.6 is phenyl or substituted aryl. The choice of onium
salt is dictated by the spectral and thermal characteristics
desired in the resist. The choice of gegenion, Y.sup.-, may be made
from a wide range of anionic species. However, properties such as
the marginal stability of, e.g., onium bisulfate or chloride salts
and the potential hazards of, e.g., arsenic, phosphorous, boron, or
antimony to the integrity of the circuits being fabricated, cause
anions such as HSO.sub.4.sup.-, Cl.sup.-, BF.sub.4.sup.-,
PF.sub.6.sup.-, AsF.sub.6.sup.-, or SbF.sub.6.sup.- to be less
desirable than anions such as triflate (CF.sub.3 SO.sub.3.sup.-) or
methane sulfonate or, generally RSO.sub.3.sup.- where R is alkyl,
aryl, or substituted alkyl or aryl. The principal characteristic of
the gegenion is, however, that it be the conjugate base of a strong
acid so that the equilibrium
will be such that the protons generated by exposure and subsequent
reaction of the onium salt are not "consumed" to give primarily HY
but remain available to attack the acid labile blocking group
attached to the imide.
It is recognized that the choice of latent photoacid (or even
gegenion in the case of onium salt) may effect the rate of
reaction, or the diffusion of the photogenerated acid from the
initially irradiated zone, in ways dependent on both the photoacid
itself and on the nature of the blocked polymer; this may effect
the imaging properties of the resist. Further, the choice of
photoacid (or gegenion in the case of onium salt) may result in
imparting excessive hydrophobic or hydrophilic character to the
resist film, which can overwhelm the properties of the imide
(and/or blocked imide) containing polymer in such a way as to
render the resist inoperable.
In order that the invention may be more fully understood, the
following examples are set forth for the purpose of illustration.
The specific enumeration of details, however, should not be
interpreted as a limitation, except as expressed in the appended
claims.
EXAMPLE 1
Preparation of Blocked Polymer
Maleimide styrene copolymer (2.00 g) was dissolved in dry
tetrahydrofuran (THF) (20 ml). After the polymer had dissolved,
tert-butyl alcohol was added (4.0 ml) and the mixture was cooled to
a temperature of 0 to 5.degree. C. Then a solution of potassium
tert-butoxide (1.20 g) dissolved in THF (5.0 ml) was added over a
period of 10 minutes, with vigorous stirring, so that the
temperature remained below 5.degree. C. After a total of 40 minutes
stirring, di-tert-butyl dicarbonate (2.20 g), with a few ml of THF
added to prevent solidification, was added all at once and the
mixture was warmed to 30.degree. C. and stirred for 4 hours.
Finally, the gelatinous mass was poured into distilled water (200
ml) with vigorous stirring, allowed to settle for 30 minutes and
filtered. The filtrate was washed with water (200 ml) then methanol
(200 ml) and dried at room temperature under a stream of nitrogen.
The polymer (2.4 g) was shown by .sup. 1 H NMR to have at least 90%
of its imide N-H groups blocked with tert-butyloxycarbonate,
##STR26##
Preparation of the Photoacid Sensitizer
Diphenyliodonium chloride (2.00 g) was dissolved in methanol (30
ml). Then silver triflate (1.70 g) dissolved in methanol (10 ml)
was added to it, with stirring. After a few minutes the solid
silver chloride was removed by filtration and the methanol was
removed under vacuum. The crude product was recrystallized from
water (40 ml) and allowed to dry at room temperature over night.
The recrystallized diphenyliodonium triflate weighed 2.34 g (86%
yield) (m.p. 183-185.degree. C.).
Preparation of Photoresist Films
Blocked maleimide styrene copolymer (1.80 g) and diphenyl iodonium
triflate sensitizer (0.20 g) were dissolved in diglyme (5.4 g) by
stirring the mixture at room temperature. Then the solution was
forced through a 0.2 .mu.m membrane filter to remove particulates.
This solution, when spin-cast at 5,000 RPM, would provide a film
1.2 .mu.m thick.
Wafers were spin-coated on a Headway Research spinner and baked at
80.degree. C. for 20 minutes to remove solvent.
Exposure and Development of Resist Film
Two inch resist-coated wafers were exposed (contact print) through
a 260.+-.15 nm interference filter and an Optoline step tablet
mask. The energy incident at the wafer surface was estimated by use
of an Eppley calibrated thermopile.
Five and six inch wafers were exposed with a Perkin-Elmer
Micralign.TM.-b 500, or 600-HT, scanning projector operating in the
UV-2 band.
After exposure, the wafers were baked in a forced convection oven
at 130.degree. C. for a period of 3 minutes to allow the
photoinduced acid to de-block the imides. Then they were developed
in 0.1 M aqueous hydroxide solution (50:50 tetramethylammonium
hydroxide and tetrabutylammonium hydroxide), rinsed with deionized
water and dried under a stream of filtered nitrogen. The contact
printed 2 inch wafers showed a sensitivity of 18 to 20 mJcm.sup.-
2, 1 .mu.m features were clearly reproduced with flat tops and
vertical side walls. The contrast was high -.gamma..gtoreq.8, with
.gamma. being defined as in G. N. Taylor, "Guidelines for
Publication of High Resolution Resist Parameters", Solid State
Technology (1984) June, p. 105, Section G.2.a). The projection
printed wafers were properly exposed in a scan time of from 11 to
20 seconds and submicron features (3/4.mu.m) were easily formed
with flat tops and nearly vertical side walls.
Without further processing, the wafers could be heated to
230.degree. C. without rounding of the photoresist features.
EXAMPLE 2
A resist was prepared in the manner of Example 1 except that the
sensitizer used was triphenyl sulfonium triflate. This sensitizer
has absorbance at longer wavelengths of light which extends the
utility of the resist from the DUV to the Mid UV region (250-350
nm). Resist films were prepared on 2-inch silicon substrates as
detailed in Example 1. The resist-coated wafers were exposed
(contact print) to either 260 nm light as in Example 1, or to
narrow band 313 nm light (again, through an interference filter).
After exposure, the wafers were baked at 110.degree. C. for 7
minutes. After baking, they were developed and rinsed as in Example
1. Wafers exposed at both wavelengths showed a sensitivity of 25
mJcm .sup.-2 with 1 micron features clearly resolved. This example
demonstrates a method of tailoring the sensitizer to a desired
spectral region.
EXAMPLE 3
A blocked polymer was prepared as in Example 1, except that the
copolymer used was maleimide-co-tertbutyl styrene. After blocking,
the polymer was used to prepare a resist as in Example 1. This
resist was used to prepare films on 2-inch silicon substrates as in
Example 1. The resist-coated silicon wafers were exposed (contact
print) to 260.+-.15 nm light through an Optoline step tablet
resolution mask. After exposure, the wafers were baked for 1 hour
at 100.degree. C. After baking, the wafers were developed in 0.35N
aqueous tetramethylammonium hydroxide solution, rinsed with
deionized water and dried under a stream of filtered nitrogen. The
contact printed wafers showed a sensitivity of 15 mJcm.sup.-2 and 1
micron features were clearly reproduced. The contrast of the resist
was very high (-.gamma.>6). There was no loss of film thickness
in the unirradiated areas during the development. This example
shows that the comonomer to maleimide in the polymer can be other
than styrene.
EXAMPLE 4
A resist was prepared in the manner of Example 1. The resist was
coated onto 3-inch oxide-coated silicon wafers in the manner of
Example 1. The resist-coated wafers were exposed to X-ray
irradiation through a gold on tantalum mask. The X-rays were
produced by a rotating tungsten source (8000 RPM) with a 2 mm spot
size. The source power was 10 kV at 600 mA. The wafers were exposed
through the mask for 8 minutes then baked for 5 minutes at
120.degree. C. After baking, the wafers were developed in the
manner of Example 1. The resist developed in a positive tone with
very high contrast and imaged 1 micron features.
EXAMPLE 5
A resist was prepared, coated on 2-inch silicon wafers and exposed
in the manner of Example 1. After exposure, the wafers were baked
for 45 seconds to 1 minute at 160.degree. C., then developed as in
Example 1. The sensitivity of resists processed in this manner was
15 to 17.5 mJcm.sup.-2 with high contrast and <1% film loss in
the unirradiated areas during development. One micron features with
vertical sidewalls were easily resolved. This example shows that
the bake time can be adjusted by varying the bake temperature,
without undue loss of resist performance.
EXAMPLE 6
A resist was prepared, coated on 2-inch silicon wafers and exposed
(contact print) in the manner of Example 1. The exposed wafer was
baked in the manner of Example 5. After baking, the wafer was
developed in 0.1N potassium hydroxide. The sensitivity of the
resist was 13 mJcm.sup.-2 and the contrast was high. One micron
features were easily resolved. This example shows that metal ion
developers will also serve to develope the exposed and baked
resist.
EXAMPLE 7
A resin was prepared in the manner of Example 1. It was compounded
in a resist as in Example 1, except that the sensitizer was a
conventional diazonaphthoquinone sensitizer
(4-benzoyl-1,3-phenylene ester of
3-diazo-3,4-dihydro-4-oxo-1-naphthalene sulfonic acid). The resin
to sensitizer ratio was 7:1. The resist was coated and exposed
(contact print) as in Example 1. The exposed wafers were baked for
1 hour at 100.degree. C. and then developed in 0.1 to 0.3N
tetramethyl ammonium hydroxide, rinsed with deionized water and
dried under a nitrogen stream. The sensitivity of the resist was 48
mJcm.sup.-2 and 1 .mu.m features were resolved. The contrast was
lower than in Example 1, -.gamma.=2.
EXAMPLE 8
A resin was prepared in the manner of Example 1. It was compounded
in a resist in the manner of Example 1 except that the sensitizer
was triphenylsulfonium hexafluoroarsenate. The resist was coated on
2-inch silicon wafers and exposed (contact print) as in Example 1.
The exposed wafers were baked for 1 hour at 100.degree. C. and then
developed in either 0.1N aqueous tetramethyl ammonium hydroxide or
0.1N aqueous potassium hydroxide. The sensitivisty of the resist
was 32 mJcm.sup.-2 and the contrast was high with -.gamma.=4. One
micron features were resolved.
EXAMPLE 9
A resist was prepared in the manner of Example 8, except that the
sensitizer was diphenyliodonium hexafluorophosphate. The resist was
coated on 2-inch silicon wafers and exposed in the manner of
Example 1 (contact print), then baked and developed in the manner
of Example 8. The sensitivity of the resist was 56 mJcm.sup.-2 and
-.gamma.was >10. One micron features were resolved.
EXAMPLE 10
Resist coated 2-inch silicon wafers were prepared in the manner of
Example 8. After the normal softbake to remove the solvent the
wafers were exposed with a krypton fluoride excimer laser operating
at 248 nm. The projection optics provided a 5:1 reduced image of a
chrome on quartz photomask to produce an irradiated pattern of 1
.mu.m lines and spaces on the resist. The total fluence of 248 nm
light on the resist was approximately 100 mJcm.sup.-2, delivered in
three pulses. After the exposure, the wafers were baked for 1 hour
at 100.degree. C. and then developed in 0.15N aqueous hydroxide
solution (50:50 tetramethyl ammonium hydroxide and tetrabutyl
ammonium hydroxide). One micron lines and spaces were easily
resolved.
EXAMPLE 11
A resist was prepared in the manner of Example 1, except that the
sensitizer was triphenylsulfonium triflate. The resist was coated
on oxide-coated, 5-inch silicon wafers in the manner of Example 1.
The wafers were exposed with a Perkin-Elmer Micralign.TM.-500 in
the UV-3 band. After exposure, the wafers were baked for 6 minutes
at 120.degree. C. After baking, the wafers were developed in the
manner of Example 1. One micron features were resolved.
EXAMPLE 12
A resist was prepared in the manner of Example 1. The resist was
coated on oxide-coated, 5-inch silicon wafers in the manner of
Example 1. The wafers were exposed with a Perkin-Elmer
Micralign.TM.-500 in the UV-2 band. The scan time for proper
exposure was approximately 20 seconds. After exposure, the wafers
were baked for 150 seconds on a commercial vacuum hotplate at
130.degree. C. After baking, the wafers were developed in the
manner of Example 1. Submicron features (3/4 .mu.m lines and
spaces) were easily resolved with flat tops and nearly vertical
sidewalls.
EXAMPLE 13
A resist was prepared in the manner of Example 1. The resist was
coated on oxide-coated (SiO.sub.2), 5-inch silicon wafers in the
manner of Example 1. The wafers were exposed with a Perkin-Elmer
Micralign.TM.-500 in the UV-2 band. After exposure, the wafers were
baked for 6 minutes at 120.degree. C. and developed in the manner
of Example 1. A wafer with the resist pattern on it was placed in a
Perkin-Elmer OmniEtch.TM. and the photoresist pattern was
transferred into the silicon dioxide substrate by reactive ion
etching. After etching, the wafer was broken and examined by
scanning electron microscopy. The SEM photos showed that the
pattern of submicron (3/4 .mu.m) lines and spaces in the
photoresist had been accurately etched into the substrate with
nearly vertical sidewalls and no rounding of the resist edges.
EXAMPLE 14
A resin was prepared in the manner of Example 1, except that 0.6 gm
of potassium tert-butoxide dissolved in THF (5.0 ml) were used.
After reaction, 50% of the imide groups were blocked and 50%
remained unblocked. The percentage of blocking was determined by
proton nuclear magnetic resonance (nmr). This resin was compounded
in a resist, coated on 2-inch silicon wafers and exposed in the
manner of Example 1. The 2-inch, contact printed wafers displayed a
sensitivity of 21 mJcm.sup.-2 and very high contrast when baked for
10 minutes at 120.degree. C. and developed in 0.1N potassium
hydroxide. The film retention in the unirradiated areas was 70%.
One micron lines were easily resolved. This example illustrates
that incompletely blocked, imide-containing polymer can be made to
function as a high contrast photoresist.
EXAMPLE 15
A resin was prepared in the manner of Example 1 such that at least
90% of the imide functionalities were blocked by
tert-butyloxycarbonate groups (as shown by proton nmr). This resin
was baked for 10 minutes at 120.degree. C. in order to partially
deblock it by thermal cleavage. The resin was shown to be only 70%
blocked after baking by proton nmr and by weight loss calculations.
This resin was then compounded in a resist in the manner of Example
1. The resist was coated on 2-inch silicon wafers and exposed
(contact print) in the manner of Example 1. After exposure, the
wafers were baked 4 minutes at 130.degree. C. then developed in the
manner of Example 1. The resist showed a sensitivity of 17 to 20
mJcm.sup.-2 with high contrast. One micron features were easily
resolved. The unirradiated areas of the film lost only 1% of their
thickness in the development step. This example shows that the
percentage blocking of a polymer can be reduced by a thermal
deblocking process in order to adjust the properties of the resist
made from the polymer.
EXAMPLE 16
A blocked polymer was prepared in the manner of Example 1 except
that the copolymer used was maleimideco-decyl vinyl ether. After
blocking, the polymer was used to prepare a resist in the manner of
Example 1. This resist was coated onto 2-inch silicon wafers and
exposed (contact print) as in Example 1. After exposure, the
resist-coated wafers were baked for 10 minutes at 110.degree. C.
and then developed in 0.075N aqueous tetramethyl ammonium
hydroxide. The sensitivity of the resist was 240 mJcm.sup.-2 and
the film retention was 30%.
EXAMPLE 17
(Comparative)
A photoresist was compounded from a novolac resin and the
diazonaphthoquinone sensitizer of Example 7. The resin to
sensitizer ration was 8:1 and the solvent was diglyme. The resist
was filtered, spin-coated onto oxide-coated, 5-inch silicon wafers
and baked for 40 minutes at 80.degree. C. to remove the residual
spinning solvent. The resist-coated wafers were then exposed on a
Perkin-Elmer Micralign.TM.-500 in either the UV-2 (Deep UV) or UV-4
(Near UV) band. After exposure, the wafers were developed in 0.128N
aqueous potassium hydroxide for a period of 3 minutes. The
sensitivity of the novolac-based resist was 36 mJcm.sup.-2 in the
near UV region and 70 mJcm.sup.-2 in the deep UV region. Scanning
electron micrographs of the resist features showed straight
sidewalls for the near UV exposures, but sloped (45.degree. )
sidewalls for the deep UV exposures. The contrast of the resist was
measured to be -.gamma.=5.5 in the near UV and -.gamma.=1 in the
deep UV. Film retention in the unirradiated areas averaged 97%.
This example illustrates the lack of utility of novolac-based
resists in the deep UV region.
EXAMPLE 18
A resin can be prepared in the manner of Example 1 except that the
copolymer used is a copolymer of maleimide and 4-methylstyrene or
4-ethylstyrene or 4-isopropylstyrene or 2,4-dimethylstyrene or
4-n-butylstyrene or .alpha.-methylstyrene or n-butyl vinyl ether or
tert-butyl vinyl ether or n-hexyl vinyl ether or n-octyl vinyl
ether or 2-ethylhexyl vinyl ether or n-decyl vinyl ether or
n-dodecyl vinyl ether or n-tetradecyl vinyl ether or n-hexadecyl
vinyl ether or n-octadecyl vinyl ether. After the polymer is
blocked in the manner of Example 1, it can be compounded in a
resist, coated, exposed, baked and developed in the manner of
Example 1 in order to provide a relief image in the resist on the
substrate. The melting point of the features will be determined by
the glass transition temperature (Tg) of the copolymer.
EXAMPLE 19
A resin can be prepared in the manner of Example 1 except that the
polymer to be blocked is a homopolymer of maleimide. The blocked
homopolymer can then be compounded in a resist and further
processed as in Example 1, except that the melting point of the
resist features will be determined by the Tg of the
homopolymer.
EXAMPLE 20
A resin can be prepared in the manner of Example 1, except that the
polymer to be blocked contains polydimethylglutarimide. The blocked
imide polymer can then be compounded in a resist and further
processed as in Example 1. The melting point of the features will
be determined by the Tg of the polydimethylglutarimide.
EXAMPLE 21
A resin can be prepared in the manner of Example 1 where the
blocking group is the benzyloxycarbonyl group (--CO.sub.2
--CH.sub.2 --C.sub.6 H.sub.5), by reacting the imide anion salt
(the intermediate product formed by reacting the imide-containing
polymer with potassium tert-butoxide as in Example 1) with benzyl
chloroformate. Once the polymer is blocked, it can be compounded in
a resist and further processed in the manner of Example 1.
EXAMPLE 22
The polymer of Example 1 can be formed by alternate synthetic
routes. For example, N-[tert-butyloxycarbonyl] maleimide is
copolymerized with styrene by heating a cyclohexanone solution of
styrene and N-blocked maleimide, in the presence of
azobisisobutyronitrile, to 60.degree. C. for 10 hours. The polymer
is isolated by pouring the cyclohexanone solution into water and
filtering the precipitated polymer.
EXAMPLE 23
Resist coated wafers are prepared in the manner of Example 1, then
exposed to a source of electron beam irradiation. After exposure,
the wafers are baked and developed in the manner of Example 1 to
yield a relief pattern in the photoresist on the substrate.
EXAMPLE 24
Di-4-methylphenyl iodonium chloride is dissolved in methanol.
Silver triflate, dissolved in methanol, is added to this solution
with stirring. After a few minutes, the solid silver chloride is
removed by filtration and the methanol is removed under vacuum.
This photoacid sensitizer is then used according to the method of
Example 1 except that the spectral range to which the resist is
sensitized is shifted 15 nm to the red. This example shows how aryl
substituents in the iodonium salt may be used to alter the spectral
sensitivity of the resist.
EXAMPLE 25
The photoresist of Example 1 can be prepared, coated, exposed
(260.+-.15 nm, 100 mJcm.sup.-2) and baked in the manner of Example
1. The baked wafer contains nonpolar areas where the resist is
still blocked (unirradiated areas) and polar areas where the imides
have been unblocked (irradiated areas). The wafer is developed in a
non-polar developer (methylene chloride) in order to remove the the
non-polar areas and leave the polar areas in place on the
substrate. The result is an image reversal of the original
irradiation pattern, that is, those areas remain which would have
been developed away in an aqueous alkaline developer.
EXAMPLE 26
The photoresist of Example 1 is further sensitized with a small
amount of an organic dye (perylene). The doubly sensitized resist
is then coated on 2-inch silicon wafers in the manner of Example 1.
The coated wafers are then processed according to the method of
Example 1, except that the spectral range to which the resist is
sensitized includes the absortion bands of perylene. This example
shows how a secondary sensitizer is used to extend the spectral
sensitivity of the resist to wavelengths where the latent photoacid
sensitizer does not absorb.
While particular embodiments of the invention have been described,
it will be understood, of course, that the invention is not limited
thereto since many modifications may be made, and it is, therefore,
contemplated to cover by the appended claims any such modifications
as fall within the true spirit and scope of the invention.
* * * * *